This invention pertains to cells for the propagation of adenoviral vectors.
Recombinant eukaryotic viral vectors have become a preferred means of gene transfer for many researchers and clinicians. The human adenovirus is one of the most widely used recombinant viral vectors in current gene therapy protocols. As the use of adenoviral vectors becomes more prevalent, the need for systems that efficiently produce adenoviral vectors suitable for administration is increasingly important.
A concern associated with recombinant adenoviral vectors is uncontrolled propagation of the vector upon administration. To address this concern, replication-deficient adenoviral vectors, typically lacking the essential E1 region of the adenoviral genome, have been developed. The relatively small foreign gene insert capacity of E1-deleted adenoviral vectors has led to the development of adenoviral vectors with additional early region gene deletions, particularly deletions in the E4 region (see, e.g., WO 96/18418 and U.S. Pat. No. 6,127,175). Such vectors are propagated in complementing cell lines expressing adenoviral E1 and E4 gene products, such as those described by Wang et al., Gene Ther., 2, 775-783 (1995), and Yeh et al., J. Virol., 70, 559-565 (1996).
Adenoviral vector technology is also limited by the difficulties associated with large-scale propagation of adenoviral vectors using currently available complementing cell lines. For example, while the A549 cell line supports sufficient propagation of wild-type adenovirus, adenoviral propagation is significantly reduced or nonexistent when A549 cells are engineered to constitutively express E1 gene products for complementation (see, e.g., Imler et al., Gene Ther., 1, 75-84 (1996), and Gao et al., Human Gene Ther., 11, 213-219 (2000)). Moreover, propagation of wild-type adenovirus on the widely used HEK 293 cell line (Graham et al., J. Gen. Virol., 36, 59-72 (1977)) results in approximately 50-75% of the yield of wild-type adenovirus on A549 cells.
Accordingly, there remains a need for alternative cells for propagating replication-deficient adenoviral vectors. The invention provides such cells. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.
The invention provides a cell having a cellular genome comprising at least one adenoviral nucleic acid sequence, which upon expression produces a gene product that complements in trans for a deficiency in at least one essential gene function of one or more regions of an adenoviral genome so as to propagate a replication-deficient adenoviral vector comprising an adenoviral genome deficient in the at least one essential gene function of the one or more regions when present in the cell. The cell (i) is a pleural effusion, large cell lung carcinoma, (ii) is epithelial, and (iii) comprises a wild-type p53 gene. Alternatively, the cell (i) is a lung carcinoma, (ii) comprises a homozygous deletion of the p53 gene, and (iii) is heterozygous for a K-ras codon 12 mutation. The inventive cell preferably is an NCI-H460 cell or a Calu-1 cell.
The invention also provides a system comprising the inventive cell and a replication-defective adenoviral vector comprising an adenoviral genome deficient in the at least one essential gene function of the one or more regions. The invention further provides a method of propagating a replication-deficient adenoviral vector, wherein the method comprises providing the inventive cell, introducing a replication-deficient adenoviral vector into the inventive cell, and maintaining the cell to propagate the replication-deficient adenoviral vector.
The invention provides a cell having a cellular genome comprising at least one adenoviral nucleic acid sequence, which upon expression produces a gene product that complements in trans for a deficiency in at least one essential gene function of one or more regions of an adenoviral genome of a replication-deficient adenoviral vector so as to propagate (i.e., replicate the entire life cycle of, or replicate to any stage of the life cycle of) the replication-deficient adenoviral vector when present in the cell.
The cell (i) is a large cell lung carcinoma derived from a pleural effusion (i.e., a pleural effusion, large cell lung carcinoma), (ii) is epithelial, and (iii) comprises a wild-type p53 gene. By xe2x80x9cderivedxe2x80x9d from a pleural effusion is meant that the cell is isolated from a large cell lung carcinoma that originated from an effusion of the lung pleura. By xe2x80x9cepithelialxe2x80x9d is meant that the cell participates in lining the inner and outer surfaces of the organism from which it is isolated. The cell has a wild-typep53 gene in that the nucleic acid sequence encoding the p53 gene does not comprise any alterations that change the normal function of the p53 gene product in the inventive cell. Advantageously, the cell comprises a homozygous K-ras codon 12 mutation. The cell comprises a homozygous K-ras codon 12 mutation in that both alleles of the K-ras gene locus are mutated in the inventive cell. Moreover, the cell does not express the p16INK4a protein. The cell also desirably exhibits adherent growth in culture, and comprises two X chromosomes and two Y chromosomes.
The cell alternatively (i) is a lung carcinoma, (ii) comprises a homozygous deletion of the p53 gene, and (iii) is heterozygous for a K-ras codon 12 mutation. The cell comprises a homozygous deletion of the p53 gene in that both alleles of the p53 gene locus comprise deletions which, for example, prevent expression of the p53 gene product or render the p53 gene product non-functional. The cell is heterozygous for a K-ras codon 12 mutation in that the cell comprises a K-ras gene locus comprising a wild-type allele and a codon 12 mutation in the other allele. Advantageously, the cell does not express the p16INK4a protein. The cell also desirably exhibits adherent growth in culture. Desirably, the antigen expression profile of the cell comprises (i) blood type A, (ii) Rh positive, and (iii) HLA antigens A10, A11, B15, and Bw35. By xe2x80x9cantigen expression profilexe2x80x9d is meant the collection of antigens that are expressed on the surface of the inventive cell.
The cell can be any suitable such cell into which can be incorporated and preferably retained the adenoviral nucleic acid encoding at least one gene product which complements in trans for a deficiency in at least one essential gene function of one or more regions of an adenoviral genome. The cell desirably can propagate adenoviral vectors and/or adeno-associated viral (AAV) vectors when infected with such vectors or with nucleic acid sequences encoding the adenoviral or AAV genome. Most preferably, the cell can propagate a suitable replication-deficient adenoviral vector upon infection with an appropriate replication-deficient adenoviral vector or transfection with an appropriate replication-deficient viral genome. The cell preferably is an NCI-H460 cell or a Calu-1 cell having a cellular genome comprising at least one adenoviral nucleic acid sequence, which upon expression produces a gene product that complements in trans for a deficiency in at least one essential gene function of one or more regions of an adenoviral genome of a replication-deficient adenoviral vector so as to propagate the replication-deficient adenoviral vector when present in the cell.
Particularly desirable cell types are those that support high levels of wild-type adenovirus propagation. The cell desirably produces at least about 100% more wild-type adenovirus, preferably at least about 200% more wild-type adenovirus, and most preferably at least about 300% more wild-type adenovirus, than a 293 cell. The cell also desirably produces at least about 90% more wild-type adenovirus, more preferably at least about 100% more wild-type adenovirus, and most preferably at least about 130% more wild-type adenovirus, than an A549 cell. The cell preferably produces at least about 8,000 focus-forming units (FFU) per cell. More preferably, the cell produces at least about 15,000 FFU per cell. Most preferably, the cell produces at least about 30,000 (e.g., at least about 35,000, 40,000, 50,000, or more) FFU per cell.
The cell comprises at least one adenoviral nucleic acid sequence as described herein, i.e., the cell can comprise one adenoviral nucleic acid sequence as described herein or more than one adenoviral nucleic acid sequence as described herein (i.e., two or more adenoviral nucleic acid sequences). Such cell lines can be generated in accordance with standard molecular biological techniques as described in International Patent Application WO 95/34671 and U.S. Pat. No. 5,994,106. The adenoviral nucleic acid sequence preferably is stably integrated into the nuclear genome of the cell. The adenoviral nucleic acid sequence preferably is retained in the cellular genome (and the adenoviral nucleic acid sequence, upon expression, preferably produces a gene product complementing in trans for a deficiency in at least one essential gene function of one or more regions of an adenoviral genome) for at least about 10, more preferably at least about 20, passages in culture (e.g., at least about 30, 40, 100, or more passages). Not to adhere to any particular theory, it is believed that genomic integration of the adenoviral nucleic acid sequence encoding the complementing factor is required to generate stable cell lines for adenoviral vector production. Additionally, complementation by transient transfection employs both labor-intensive and inconsistent techniques, resulting in low adenovirus yield and difficulty associated with large-scale viral production. Although stable integration of the adenoviral nucleic acid sequence is preferred, the adenoviral nucleic acid sequence can reside, for example, on a plasmid, liposome, or any other type of molecule that can harbor an adenoviral nucleic acid sequence extrachromosomally. The introduction and stable integration of the adenoviral nucleic acid sequence into the genome of the cell requires standard molecular biology techniques that are well within the skill of the art, such as those described in Sambrook et al., Molecular Cloning, a Laboratory Manual, 2d ed., Cold Spring Harbor Press, Cold Spring Harbor, N.Y. (1989), Watson et al., Recombinant DNA, 2d ed., Scientific American Books (1992), and Ausubel et al., Current Protocols in Molecular Biology, Wiley Interscience Publishers, NY (1995).
The xe2x80x9cadenoviral nucleic acid sequencexe2x80x9d can be any nucleic acid sequence that is obtained from, derived from, or based upon an adenoviral nucleic acid sequence. A sequence is xe2x80x9cobtainedxe2x80x9d from a source when it is isolated from that source. A sequence is xe2x80x9cderivedxe2x80x9d from a source when it is isolated from a source but modified in any suitable manner (e.g., by deletion, substitution (mutation), insertion, or other modification to the sequence) so as not to disrupt the normal function of the source gene. A nucleic acid sequence is xe2x80x9cbased uponxe2x80x9d a source when the sequence is a sequence more than about 70% homologous (preferably more than about 80% homologous, more preferably more than about 90% homologous, and most preferably more than about 95% homologous) to the source but obtained through synthetic procedures (e.g., polynucleotide synthesis, directed evolution, etc.). Identifying such homologous sequences can be accomplished using any suitable method, particularly through use of the GenBank sequence databases provided by the National Center for Biotechnology Information (NCBI). Determining the degree of homology, including the possibility for gaps, can be accomplished using any suitable method (e.g., BLASTnr, provided by GenBank).
The adenoviral nucleic acid sequence can be obtained or derived from the same or different serotype of adenovirus as the adenoviral vector to be propagated in the cell. The adenoviral nucleic acid sequence and the adenoviral vector preferably are obtained from a group C adenovirus, more preferably from a serotype 2 or 5 adenovirus. Moreover, the adenoviral nucleic acid sequence can include one or more mutations (e.g., point mutations, deletions, insertions, etc.) from the corresponding naturally occurring adenoviral coding sequence. Thus, where mutations are introduced in the adenoviral nucleic acid sequence to effect one or more amino acid substitutions in an encoded gene product, such mutations desirably effect such amino acid substitutions whereby codons encoding positively-charged residues (H, K, and R) are substituted with codons encoding positively-charged residues, codons encoding negatively-charged residues (D and E) are substituted with codons encoding negatively-charged residues, codons encoding neutral polar residues (C, G, N, Q, S, T, and Y) are substituted with codons encoding neutral polar residues, codons encoding neutral non-polar residues (A, F, I, L, M, P, V, and W) are substituted with codons encoding neutral non-polar residues. Such mutations can also be introduced to effect one or more amino acid substitutions in the N- or C-terminus of the encoded non-adenoviral gene product.
The adenoviral nucleic acid sequence can be any suitable nucleic acid sequence as described herein that, upon expression, produces one or more gene products that complement for one or more deficiencies in any adenoviral essential gene functions (i.e., functions necessary for adenovirus propagation). By xe2x80x9ccomplements for a deficiency in an essential gene function of an adenoviral genomexe2x80x9d is meant that the gene product encoded by the adenoviral nucleic acid sequence exhibits an adenoviral gene function that is essential (i.e., necessary) for an adenoviral vector to propagate in a cell. For example, the gene product can induce transcription of promoters regulated by the E1A protein, such as the E2A promoter.
The gene product encoded by the adenoviral nucleic acid sequence can be an RNA sequence or a protein (e.g., a peptide or a polypeptide). Preferably, the gene product encoded by the adenoviral nucleic acid sequence is a protein.
The adenoviral nucleic acid sequence, upon expression, produces at least one gene product that provides an adenoviral essential gene function, i.e., that complements in trans for one or more deficiencies in any adenoviral essential gene function (i.e., a function that is necessary for adenovirus propagation). The adenoviral nucleic acid sequence, upon expression, can produce a gene product that complements for two or more deficiencies in adenoviral essential gene functions (from the same or different regions of the adenoviral genome). The adenoviral nucleic acid sequence, upon expression, can produce two or more gene products, each of which complements for a deficiency (i.e., at least one deficiency, including but not limited to, two or more deficiencies) in adenoviral essential gene functions (from the same or different regions of the adenoviral genome).
Essential adenoviral gene functions are those gene functions that are required for propagation (i.e., replication) of a replication-deficient adenoviral vector. Essential gene functions are encoded by, for example, the adenoviral early regions (e.g., the E1, E2, and E4 regions), late regions (e.g., the L1-L5 regions), genes involved in viral packaging (e.g., the IVa2 gene) and virus-associated RNAs (e.g., VA-RNA I and/or VA-RNA II). Thus, the gene product encoded by the adenoviral nucleic acid sequence complements for a deficiency in at least one adenoviral essential gene function encoded by the early regions, late regions, viral packaging regions, virus-associated RNA regions, or combinations thereof, including all adenoviral functions (e.g., to enable propagation of adenoviral amplicons comprising only inverted terminal repeats (ITRs) and the packaging signal or only ITRs and an adenoviral promoter).
The gene product desirably complements for a deficiency in at least one essential gene function of one or more regions of the adenoviral genome selected from the early regions, e.g., the E1, E2, and E4 regions. Preferably, the gene product complements in trans for a deficiency in at least one essential gene function of the E1 region of the adenoviral genome. More preferably, the gene product complements in trans for a deficiency in at least one essential gene function of an adenoviral E1A coding sequence and/or an adenoviral E1B coding sequence (which together comprise the E1 region). In that respect, one gene product can complement in trans for a deficiency in at least one essential gene function of the E1A coding sequence and another (i.e., different) gene product can complement in trans for a deficiency in at least one essential gene function of the E1B coding sequence. In addition or alternatively to the gene product(s) complementing in trans for the aforementioned deficiencies in adenoviral essential gene functions, the same or different gene product(s) can complement for a deficiency in at least one essential gene function of the E2 (particularly the adenoviral DNA polymerase and terminal protein) and/or E4 regions of the adenoviral genome. Desirably, a cell that complements for a deficiency in the E4 region comprises the E4-ORF6 gene sequence and produces the E4-ORF6 protein. Such a cell desirably comprises at least ORF6 and no other ORF of the E4 region of the adenoviral genome.
Although not preferred, a helper virus can be provided to the cell in the event that the cell does not complement for all deficiencies in essential gene functions of the adenoviral genome of the adenoviral vector to be propagated. The helper virus contains coding sequences that, upon expression, produce gene products which provide in trans those gene functions that are necessary for adenoviral propagation (e.g., the IVa2 gene function). In other words, the helper virus can comprise any adenoviral nucleic acid sequence that is not required in cis (e.g., the ITRs and packaging signal) for propagation.
The cell can further comprise an xe2x80x9cenhancingxe2x80x9d nucleic acid sequence which upon expression produces at least one gene product that enhances propagation of a replication-deficient adenoviral vector without necessarily complementing for a deficiency in an adenoviral essential gene function, so as to propagate more replication-deficient adenoviral vectors when present in the cell than when the xe2x80x9cenhancingxe2x80x9d nucleic acid sequence is absent from the cell. Although genomic integration of this xe2x80x9cenhancingxe2x80x9d nucleic acid sequence is preferred, the xe2x80x9cenhancingxe2x80x9d nucleic acid sequence also can be maintained in the cell extrachromosomally (e.g., on a plasmid).
The xe2x80x9cenhancingxe2x80x9d nucleic acid sequence can be an adenoviral nucleic acid sequence that encodes at least one adenoviral gene product. In particular, the adenoviral gene product can be a protein encoded by, for example, the E1, E2, or E4 regions. The adenoviral gene product also can be a protein encoded by the late regions of the adenoviral genome, such as those encoded by the L1-L5 regions. Alternatively, the xe2x80x9cenhancingxe2x80x9d nucleic acid sequence can encode the adenoviral IVa2 protein, the pIX protein, or virus-associated RNA (e.g., VA-RNA I or II). The xe2x80x9cenhancingxe2x80x9d nucleic acid sequence also can be an animal or non-adenoviral nucleic acid sequence. The xe2x80x9cenhancingxe2x80x9d nucleic acid sequence can encode, for example, an animal protein that inhibits and/or prevents apoptosis (e.g., Bcl-2). Moreover, the xe2x80x9cenhancingxe2x80x9d nucleic acid sequence can encode, for example, an RNA molecule or protein that improves the efficiency or rate of replication-deficient adenoviral vector propagation.
The expression of the adenoviral nucleic acid sequence in the cell is controlled by a suitable expression control sequence operably linked to the adenoviral nucleic acid sequence. An xe2x80x9cexpression control sequencexe2x80x9d is any nucleic acid sequence that promotes, enhances, or controls expression (typically and preferably transcription) of another nucleic acid sequence. Suitable expression control sequences include constitutive promoters, inducible promoters, repressible promoters, and enhancers. The adenoviral nucleic acid sequence can be regulated by its endogenous promoter or, in contrast, by a nonnative promoter sequence. Examples of suitable nonnative promoters include the CMV immediate early promoter, the phosphoglycerate kinase (PGK) promoter, the long terminal repeat promoter of the Rous sarcoma virus (LTR-RSV), the sheep metallothionien promoter, and the human ubiquitin C promoter. Alternatively, expression of the adenoviral nucleic acid sequence can be controlled by a chimeric promoter sequence. The promoter sequence is xe2x80x9cchimericxe2x80x9d when it comprises at least two nucleic acid sequence portions obtained from, derived from, or based upon at least two different sources (e.g., two different regions of an organism""s genome, two different organisms, or an organism combined with a synthetic sequence). In addition, the expression control sequence can be activated upon infection with a viral vector, such as a replication-deficient adenoviral vector, or contact with viral peptides. Suitable expression control sequences can be determined using eukaryotic expression systems such as are generally described in Sambrook et al., supra, and by using reporter gene systems (see, e.g., Taira et al., Gene, 263, 285-292 (2001)).
The invention also provides a system comprising the inventive cell and a replication-deficient adenoviral vector comprising an adenoviral genome deficient in the at least one essential gene function of the one or more regions (i.e., a replication-deficient adenoviral vector comprising the deficiencies complemented for by the inventive cell). The invention further provides a method of propagating a replication-deficient adenoviral vector. The method comprises providing a cell of the invention, introducing the replication-deficient adenoviral vector into the cell, wherein the replication-deficient adenoviral vector comprises an adenoviral genome deficient in the at least one essential gene function of the one or more regions, and maintaining the cell (e.g., under conditions suitable for adenoviral propagation) to propagate the adenoviral vector.
The adenoviral vector is deficient in at least one gene function (of the adenoviral genome) required for viral propagation (i.e., an adenoviral essential gene function), thereby resulting in a xe2x80x9creplication-deficientxe2x80x9d adenoviral vector. The adenoviral vector is deficient in the one or more adenoviral essential gene functions complemented for by the inventive cell to allow for propagation of the replication-deficient adenoviral vector when present in the cell.
Preferably, the adenoviral vector is deficient in at least one essential gene function of the E1 region, e.g., the E1a region and/or the E1b region, of the adenoviral genome that is required for viral replication. The recombinant adenovirus also can have a mutation in the major late promoter (MLP), as discussed in International Patent Application WO 00/00628. More preferably, the vector is deficient in at least one essential gene function of the E1 region and at least part of the nonessential E3 region (e.g., an Xba I deletion of the E3 region). The adenoviral vector can be xe2x80x9cmultiply deficient,xe2x80x9d meaning that the adenoviral vector is deficient in one or more essential gene functions in each of two or more regions of the adenoviral genome. For example, the aforementioned E1-deficient or E1-, E3-deficient adenoviral vectors can be further deficient in at least one essential gene of the E4 region and/or at least one essential gene of the E2 region (e.g., the E2A region and/or E2B region). Adenoviral vectors deleted of the entire E4 region can elicit lower host immune responses. Examples of suitable adenoviral vectors include adenoviral vectors that lack (a) all or part of the E1 region and all or part of the E2 region, (b) all or part of the E1 region, all or part of the E2 region, and all or part of the E3 region, (c) all or part of the E1 region, all or part of the E2 region, all or part of the E3 region, and all or part of the E4 region, (d) at least part of the E1a region, at least part of the E1b region, at least part of the E2a region, and at least part of the E3 region, (e) at least part of the E1 region, at least part of the E3 region, and at least part of the E4 region, and (f) all essential adenoviral gene products (e.g., adenoviral amplicons comprising ITRs and the packaging signal only). The adenoviral vector can contain a wild type pIX gene. Alternatively, although not preferably, the adenoviral vector also can contain a pIX gene that has been modified by mutation, deletion, or any suitable DNA modification procedure.
The replication-deficient adenoviral vector can be generated by using any species, strain, subtype, or mixture of species, strains, or subtypes, of an adenovirus or a chimeric adenovirus as the source of vector DNA. The adenoviral vector can be any adenoviral vector capable of growth in a cell, which is in some significant part (although not necessarily substantially) derived from or based upon the genome of an adenovirus. The adenoviral vector preferably comprises an adenoviral genome of a wild-type adenovirus of group C, especially of serotype (i.e., Ad5). Adenoviral vectors are well known in the art and are described in, for example, U.S. Pat. Nos. 5,559,099, 5,712,136, 5,731,190, 5,837,511, 5,846,782, 5,851,806, 5,962,311, 5,965,541, 5,981,225, 5,994,106, 6,020,191, and 6,113,913, International Patent Applications WO 95/34671, WO 97/21826, and WO 00/00628, and Thomas Shenk, xe2x80x9cAdenoviridae and their Replication,xe2x80x9d and M. S. Horwitz, xe2x80x9cAdenoviruses,xe2x80x9d Chapters 67 and 68, respectively, in Virology, B. N. Fields et al., eds., 3d ed., Raven Press, Ltd., New York (1996).
The construction of adenoviral vectors is well understood in the art and involves the use of standard molecular biological techniques, such as those described in, for example, Sambrook et al., supra, Watson et al., supra, Ausubel et al., supra, and other references mentioned herein. Moreover, adenoviral vectors can be constructed and/or purified using the methods set forth, for example, in U.S. Pat. No. 5,965,358 and International Patent Applications WO 98/56937, WO 99/15686, and WO 99/54441.
When the cell is used to propagate a replication-deficient adenoviral vector, it is desirable to avoid a recombination event between the cellular genome (of the cell) and the adenoviral genome (of the adenoviral vector) that would result in the generation of a replication-competent adenovirus (RCA). As such, there is preferably insufficient overlap between the genome of the cell and the replication-deficient adenoviral vector genome to mediate a recombination event sufficient to result in a replication-competent adenovirus. If overlap exists, the overlapping sequences desirably are predominantly located in the nucleic acid flanking the coding region of the complementation factor (the xe2x80x9ctrans-complementing regionxe2x80x9d) in the cellular genome and the nucleotide sequences adjacent to the missing region(s) of the adenoviral genome. Ideally, there is no overlap between the cellular genome and the adenoviral vector genome. However, it is acceptable that partial overlap exists between the cellular genome and the adenoviral vector genome on one side of the trans-complementing region. In such an event, the region of homology preferably is contiguous with the trans-complementing region. For example, when the cell comprises a trans-complementing region comprising a nucleotide sequence of the adenoviral E1 region, the cell desirably lacks homologous sequences on the 5xe2x80x2 side (left side) of the trans-complementing region corresponding to the adenoviral inverted terminal repeats (ITRs) and packaging signal sequences, but contains homologous sequences on the 3xe2x80x2 side (right side) of the trans-complementing region. The region of homology is at least about 2000 base pairs, preferably at least about 1000 base pairs (e.g., at least about 1500 base pairs), more preferably at least about 700 base pairs, and most preferably at least about 300 base pairs.
The cell preferably is characterized by lacking the 5xe2x80x2 ITR, the packaging sequence, and the E1A enhancer of the adenoviral genome. The preferred cell is further characterized by desirably comprising the nucleic acid sequences encoding E1A, EB, protein IX, and IVa2/partial E2B. In particular, the preferred cell comprises at least one adenoviral nucleic acid sequence which lacks nucleotides 1-361, yet comprises adenoviral nucleotides 3325-5708 located 3xe2x80x2 to the complementing region. Not to adhere to any particular theory, it is believed that a single recombination event in such a homologous region will not give rise to a replication competent adenoviral vector due to the absence of the 5xe2x80x2 ITR and packaging sequence. In a similar manner, a preferred cell that contains both the E1 and E4 regions sufficient to propagate E1-, E4-deleted adenoviral vectors can comprise a region of homology between the cellular genome and the adenoviral genome located 5xe2x80x2 or 3xe2x80x2 to the nucleic acid sequence encoding the E4 region.
The generation of RCA desirably is diminished such that (a) the cell produces less than about one replication-competent adenoviral vector for at least about 20 passages after infection with the adenoviral vector, (b) the cell produces less than about one replication-competent adenoviral vector in a period of about 36 hours post-infection, (c) the cell produces less than about one replication-competent adenoviral vector per 1xc3x971010 total viral particles (preferably 1xc3x971011 total viral particles, more preferably 1xc3x971012 total viral particles, and most preferably 1xc3x971013 total viral particles), or any combination of (a)-(c). Optimally, the amount of overlap between the cellular genome and the adenoviral genome (i.e., the genome of the adenoviral vector being propagated in the cell) is insufficient to mediate a homologous recombination event that results in a replication-competent adenoviral vector such that replication-competent adenoviruses are eliminated from the vector stocks resulting from propagation of the replication-deficient adenoviral vector in the cell. Virus growth yield and virus plaque formation have been previously described (see, e.g., Burlseson et al., Virology: A Laboratory Manual, Academic Press Inc. (1992)), and measuring RCA as a function of plaque forming units is described in U.S. Pat. No. 5,994,106.
The following examples further illustrate the invention but, of course, should not be construed as in any way limiting its scope.